1. Field of the Invention
Many missiles, including self propelled missiles which are fired by means of a launching tube, are equipped with vanes or fins which open out once the missile has left the launching tube.
In order to insure the greatest possible firing accuracy, it is advantageous for such a vane or fin system to open rapidly and accurately as soon as the missile has left the launching tube. Also, once the vanes or fins are open it is important that they be retained in a locked position.
The missile is fired from a launching tube, either smooth bore or rifled. This necessarily implies that the fins must be folded toward the axis of the projectile to permit the latter to travel through the tube, the fins opening out or unfolding as soon as the projectile leaves the tube.
2. Description of the Prior Art
One prior method of holding the folding fins in the deployed position was to employ a spring loaded lock pin seated in a hole at the bottom of the fin slot in the base plate of the projectile. The lock pin rides on the radius of the fin hub until the fin rotates to the deployed position. The stop pin is then forced, by the spring, into a step cut in the fin hub.
The fin hub is structurally weakened by the step cut. As the fin continues to rotate past the deployed position it strikes the fin slot end in the base plate with sufficient force to cause local yielding of both the fin and the fin slot end of the base plate. This results in fin rebound between the fin slot end and the stop pin of several cycles of approximately 30.degree.. The rebound force against the stop pin is of sufficient magnitude to cause occasional stop pin failures. When this occurs, the fin, which is still attached to the base plate by a pivot pin, trails in and is eroded by the motor exhaust plume. The non-symmetrical fin configuration induced by the failure results in highly unstable missile flight characteristics and subsequent target loss by the missile.
Another method used employs the same spring loaded stop pin seated in a blind hole in the fin hub parallel to the fin pivot pin. The stop pin rides on the fin slot face until the fin rotates to the deployed position. The stop pin is then forced by the spring into a step cut in the face of the fin slot. This configuration results in the fin being forced to one side of the fin slot as the high shear force is applied to the stop pin by rebound.
A third method employs a spring loaded stop dog mounted on a pivot pin at the bottom of the fin slot. The free end of the stop dog rides on the fin hub radius until the fin rotates to the deployed position. The spring then forces the free end of the stop dog into a step cut in the fin hub radius. The fin hub is structurally weakened by the step cut. This particular mechanism is unduly complicated and difficult to assemble as well.